Government accounting (GA) and National accounts (NA) are two reporting systems that, although aiming different purposes, are linked – public administrations financial information for the latter is provided by the former. Therefore, the alignment between the two systems is an issue for the reliability of the public sector aggregates finally obtained by the National Accounts. In the EU context, this is a critical issue, inasmuch as these aggregates are the reference for monitoring the fiscal policy underlying the Euro currency. However, while reporting in NA is accrual-based and harmonized under the European System of Regional and National Accounts, the GA each country still has its own reporting system, often mixing cash basis in budgetary reporting with accrual basis in financial reporting, hence requiring accounting basis adjustments when translating data from GA into NA.Starting by conceptually analyzing the accounting basis differences between GA and NA and the adjustments to be made when translating data from the former into the latter, this paper uses evidence from three southern European countries – Portugal, Spain and Italy, representing the southern Continental European accounting perspective, with cash-based budgetary reporting, and where budgetary deficits have been particularly significant in the latest years – to show how diversity and materiality of these adjustments may question the reliability of the budgetary deficits finally reported in NA.The main findings point to the need for standardized procedures to convert cash-based (GA) into accrual-based (NA) data as a crucial step, preventing accounting manipulation, thus increasing reliability of informative outputs for both micro and macro purposes.